youtube crashingSupport

my youtube app that came installed is crashing. it opens for 1 second, then closes. on my home shortcut, it shows as "loading" constantly.
Also, some times it will ask me for my password to log in, but it has my username incorrectly put in. i cant find a way to change my username to log into my account. when it does prompt me , it will only ask for the password as the username is already locked in there and it will not let me edit it.